Preterm infants requiring ventilatory support because of respiratory distress syndrome (RDS) will be randomly assigned to either conventional ventilation (CV) or high frequency jet ventilation (HFJV) during a 5-year longitudinal study. In all ventilated infants and in randomly selected non-ventilated infants (NV) with no or mild RDS, serial cranial ultrasound (US) studies which do not interfere with intensive care management will be performed shortly after birth and then every 48 to 72 hours until ventilatory support is discontinued. US studies will then be obtained in all survivors at 7 to 14 day intervals until discharge, and all images will be independently interpreted by 2 of the investigators, both of whom are blinded as to the treatment group (CV, HFJV or NV). The US images will be graded for intracranial hemorrhage (ICH), periventricular echodensity (PVE), and periventricular cysts (PCs) and measured for ventricular size (VS) and brain/cranial growth according to our previously established protocol. Color Doppler imaging (CDI), which depicts blood flow in color and anatomy in black and white, will be used to measure flow velocity and pulsatility of the cerebral arteries in randomly selected infants from all three groups (CV, HFJV and NV). Infants treated by CV and HFJV will be studied with CDI while on assisted ventilation and again after ventilatory support has been discontinued. The goals of this application, a continuation and extension of our present research, is to compare the relationship of two types of assisted ventilation (CV and HFJV) to brain disorders as ascertained by neonatal cranial US and CDI studies and by neurodevelopmental assessments during early childhood. The proposed research in preterm infants will test the following hypotheses: 1. Are neurosonographic abnormalities (ICH,PV,PC) more frequent or more severe in infants treated with CV than in those treated with HFJV? 2. Are cerebral growth and ventricular size as measured by cranial US correlated with type of ventilation or with perinatal complications and variables independent of type of ventilation? 3. Are cerebral blood flow patterns, velocity, and pulsatility as determined by CDI correlated with type of ventilation or with US abnormalities or with both? 4. Are measures of early development independent of the subject's SES profile correlated with type of ventilation? Our studies completed during the past three years have defined the prognostic significance of various US abnormalities through the early pre- school period. As part of this continuation proposal we plan to continue developmental studies on our previously enrolled prematurely born subjects.